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Characterization of caprock shale is critical in CO2 storage site evaluation because the caprock shale acts as a barrier for the injected buoyant CO2 plume. The properties of shales are complex and influenced by various processes; hence, it is challenging to evaluate the caprock quality. An integrated approach is therefore necessary for assessing seal integrity. In this study, we investigated the caprock properties of the Lower Jurassic Drake Formation shales from the proposed CO2 storage site Aurora (the Longship/Northern Lights CCS project), located in the Horda Platform area, offshore Norway. Wireline logs from 50 exploration wells, various 2D seismic lines, and two 3D seismic cubes were used to investigate the variations of the caprock properties. The Drake Formation was subdivided into upper and lower Drake units based on the lithological variations observed. Exhumation and thermal gradient influencing the caprock properties were also analyzed. Moreover, rock physics diagnostics were carried out, and caprock property maps were generated using the average log values to characterize the Drake Formation shales. In addiiton, pre-stack seismic-inverted properties and post-stack seismic attributes were assessed and compared to the wireline log-based analysis. The sediment source controlled at 61° N significantly influenced the depositional environment of the studied area, which later influenced the diagenetic processes and had various caprock properties. The upper and lower Drake units represent similar geomechanical properties in the Aurora area, irrespective of significant lithological variations. The Drake Formation caprock shale near the injection site shows less-ductile to less-brittle brittleness values. Based on the caprock thickness and shaliness in the Aurora injection site, Drake Formation shale might act as an effective top seal. However, the effect of injection-induced pressure changes on caprock integrity needs to be evaluated. [ABSTRACT FROM AUTHOR]

To mitigate the global warming crisis, one of the effective ways is to capture CO2 at an emitting source and inject it underground in saline aquifers, depleted oil and gas reservoirs, or in coal beds. This process is known as carbon capture and storage (CCS). With CCS, CO2 is considered a waste product that has to be disposed of properly, like sewage and other pollutants. While and after CO2 injection, monitoring of the CO2 storage site is necessary to observe CO2 plume movement and detect potential leakage. For CO2 monitoring, various physical property changes are employed to delineate the plume area and migration pathways with their pros and cons. We introduce a new rock physics model to facilitate the time-lapse estimation of CO2 saturation and possible pressure changes within a CO2 storage reservoir based on physical properties obtained from the prestack seismic inversion. We demonstrate that the CO2 plume delineation, saturation, and pressure changes estimations are possible using a combination of Acoustic Impedance (AI) and P- to S-wave velocity ratio (Vp/Vs) inverted from time-lapse or four-dimensional (4D) seismic. We assumed a scenario over a period of 40 years comprising an initial 25 year injection period. Our results show that monitoring the CO2 plume in terms of extent and saturation can be carried out using our rock physics-derived method. The suggested method, without going into the elastic moduli level, handles the elastic property cubes, which are commonly obtained from the prestack seismic inversion. Pressure changes quantification is also possible within un-cemented sands; however, the stress/cementation coefficient in our proposed model needs further study to relate that with effective stress in various types of sandstones. The three-dimensional (3D) seismic usually covers the area from the reservoir's base to the surface making it possible to detect the CO2 plume's lateral and vertical migration. However, the comparatively low resolution of seismic, the inversion uncertainties, lateral mineral, and shale property variations are some limitations, which warrant consideration. This method can also be applied for the exploration and monitoring of hydrocarbon production. [ABSTRACT FROM AUTHOR]

Rock physics analyses of data from a wildcat well 7117/9-1 drilled in the Senja Ridge area, located in the Norwegian Barents Sea, reveal changes in stiffness within the fine-grained Paleogene Sotbakken Group sediments, caused by the transformation of opal-A to opal-CT, and opal-CT to quartz. These changes manifest as flat spots on 2D seismic profiles. These flat spots were mistaken as hydrocarbon–water contacts, which led to the drilling of well 7117/9-1. Rock physics analyses on this well combined with a second well (7117/9-2) drilled further NW and updip on the Senja Ridge indicate overpressure within the opal-CT-rich zones overlying the opal-CT to quartz transformation zones in the two wells. The absence of opal-A–opal-CT and opal-CT–quartz flat spots on seismic in the second well is attributed to differences in the temperature and timing of uplift. Amplitude v. angle (AVA) modelling indicates both the opal-A–opal-CT and opal-CT–quartz interface points plot on the wet trend, whereas modelled gas–brine, oil–brine and gas–oil contacts fall within quadrant-I. These findings will be useful in understanding the nature of compaction of biogenic silica-rich sediments where flat spots could be misinterpreted as hydrocarbon-related contacts in oil and gas exploration. [ABSTRACT FROM AUTHOR]

Abstract: Regional assessment studies for CO2 storage plays have been carried out in the Norwegian-Danish Basin of the Central North Sea and in the Skagerrak-Kattegat area. The development of the reservoir models is a part of an ongoing interdisciplinary project with the overall goal to establish a basis for large-scale handling of CO2 in this area, including regional CO2 source and capture possibilities, transportation and infrastructure, possible storage sites as well as legal aspects relating to the whole CCS chain. The study shows that all the necessary premises for a safe, long term CO2 storage, are present in the area. Two trap types for storage have been studied more closely: 1) large gently inclined, unfaulted reservoirs in the northern Skagerrak area and 2) dome structures with four-way closures above salt pillows in the Norwegian Danish Basin. We have closely focused on the Upper Triassic-lowermost Jurassic Gassum Formation and the Middle Jurassic Haldager Sand Formation. The current study presents reservoir characteristics of the sandstones of the Gassum and Haldager formations in the Fjerritslev Trough and on the Skagerrak-Kattegat Platform. [Copyright &y& Elsevier]

Abstract: The controlled-source electromagnetic (CSEM) method is a proven and promising geophysical technique in the hydrocarbon exploration area. Recently, there is increasing interest in applying it to CO2-injection monitoring in both land and marine environments. For example, a marine CSEM survey has been carried out in the Sleipner area in 2008 to map the CO2 plume in the Utsira formation. There are still scientific and technical issues to resolve and improve further. In the current study, we focus on two particular issues. The first is to explore the possibility of modeling the CO2 plume in the Utsira formation at the Sleipner area by means of an effective anisotropic resistivity layer. The second is the application of so-called surface-to-borehole CSEM in order to increase the sensitivity of CSEM data to the CO2 plume. [Copyright &y& Elsevier]

Injection-induced rock mechanical failure risks are critical in CO2 sequestration, and thus there is a need to evaluate these occurrences to ensure safe and reliable subsurface storage. A stress–strain-based numerical simulation can reveal the potential mechanical risks of any CO2 sites. This study investigated the hydromechanical effect on geomechanical failure due to injection-induced stress and pore pressure changes in the prospective CO2 storage site Smeaheia, offshore Norway. An inverted-seismic-property-driven 3D field-scale geomechanical model was carried out in the Smeaheia area to evaluate the rock failure and deformation risks in various pressure-build-up scenarios. A one-way coupling between the before- and after-injection pressure scenarios of nine different models has been iterated using the finite element method. The effect of the sensitivity of total pore volume and pore compressibility on rock mechanical deformation is also evaluated. Although various models illustrated comparative variability on failure potential, no model predicted caprock failure or fracture based on the Mohr–Coulomb failure envelope. Moreover, the lateral mechanical failure variation among different locations indicated the possibility to identify a safer injection point with less chances of leakage. In addition, the pore volume and pore compressibility significantly influence the mechanical behavior of the reservoir and caprock rocks. Although this analysis could predict better injection locations based on geomechanical behavior, a fluid simulation model needs to be simulated for assessing lateral and vertical plume migration before making an injection decision. [ABSTRACT FROM AUTHOR]

Evaluating any subsurface CO 2 storage site comprises the reservoir, seal, and overburden investigation to mitigate injection and storage-related complications. The Upper-Middle Jurassic Sognefjord, Fensfjord, and Krossfjord formation sandstones are potential CO 2 storage reservoirs at the Smeaheia area, northern North Sea. The Smeaheia area is located east of the Troll oil and gas field. The Upper Jurassic organic-rich Heather and Draupne Formation shales are the main seals for the sandstone reservoirs. In this study, we carried out a prestack seismic inversion to obtain elastic property cubes of acoustic impedance (AI), velocity ratio (Vp/Vs), and bulk density (RhoB). From these elastic cubes, we obtained the reservoir properties such as porosity (Phi), shaliness (V sh), and permeability (k) of Sognefjord, Fensfjord, and Krossfjord formations. We introduced two new equations to extract the shale volume and porosity cubes from the inverted elastic cubes in the present study. These equations are nonlinear based on the AI versus Vp/Vs rock physics template. Both equations are correlated first with the well log data and then applied on the elastic property cubes (AI versus Vp/Vs) to obtain the V sh and Phi property cubes. An additional porosity cube (PhiD) was generated from the inverted RhoB for comparison. Finally, using an empirical equation, permeability was extracted from the porosity cube. The reservoir properties we derived from 3D seismic, in addition to the well log, revealed the vertical and lateral variations of porosity, shaliness, and permeability in the Smeaheia area. We used these reservoir properties to infer the depositional environment and the viability of reservoirs for CO 2 storage. The depositional environments identified were shoreface and deltaic from the extracted sand-body geometries. We found the Sognefjord Formation possessing the best reservoir properties, followed by the Fensfjord Formation as the secondary storage potential. In contrast, the Krossfjord Formation owed the lowest reservoir quality in the Smeaheia area. • Our new equations helped to reveal the lateral variations in reservoirs and their depositional environment. • The Sognefjord is the best, and Fensfjord Formation is the second-best quality reservoir in the area for CO 2 storage. • The Krossfjord Formation is the least suitable for CO 2 storage in the Smeaheia area. [ABSTRACT FROM AUTHOR]